The proportion of injection molded articles (resins) used for the outer panels and interior and exterior parts of automobiles has been increased from the viewpoint of the weight saving of the automobiles These materials (resin material compositions) have improved rigidity (tensile modulus), impact resistance (Charpy impact value), and other physical properties by adding various fillers into a matrix resin (thermoplastic polyolefin resin). Such resin material compositions are disclosed in Patent Documents 1 to 3.
A resin composition for injection molding disclosed in Patent Document 1 has improved rigidity by adding talc to a matrix resin. Although rigidity is improved, impact resistance is decreased by simply adding talc, and thus the decrease in impact resistance is compensated by further adding fibrous glass fillers (whiskers).
In a thermoplastic resin composition disclosed in Patent Document 2, not talc but a nano-inorganic filler having an average particle diameter of 300 nm or less and fibrous glass fillers are added to a matrix resin. This is because adding both talc and fibrous glass fillers (glass fibers) to the matrix resin can improve rigidity and compensate for decrease in impact resistance but causes excessively high melt viscosity (MFR), which makes it difficult to mold the thermoplastic resin composition.
In a composite material disclosed in Patent Document 3, not long fibrous glass fillers but short fibrous glass fillers are added to a matrix resin (PP resin and the like) because adding the long fibrous glass fillers to the matrix resin results in improving strength but leads to poor surface smoothness (poor appearance) due to easily impaired uniform dispersibility of the long fibrous glass fillers.